NEAAR-LARC: Evaluating a Nonessential Amino Acid Restriction (NEAAR) Medical Food With Total Neoadjuvant Therapy for Locally Advanced Rectal Cancer (LARC)

* Histologically confirmed diagnosis of adenocarcinoma of the rectum

* Clinical stage II (cT3-4, N-) or Stage III (cT any, N+) based on MRI

* Eligible for total mesorectal excision

* No evidence of distant metastasis

* No prior pelvic radiation therapy

* No prior chemotherapy

* Age ≥18 years

* Patients unable to undergo MRI

* Other anticancer or experimental therapy

* Body mass index (BMI) <18.5 kg/m2 or >40 kg/m2

* Serious or refractive cachexia or anorexia

* Insulin-dependent diabetes Taking or needs to take any protein or amino acid containing nutritional supplements (e.g., Ensure®) Patients with a condition where high-fat or fatty food is contraindicated History of confirmed food allergy Active wound or skin graft that would require a significant increase in protein requirements for skin integrity and healing